Photoelectric conversion element and method for producing the same

ABSTRACT

A photoelectric conversion element capable of reducing a specific dark current. In a photoelectric conversion element ( 10 ) including an anode ( 12 ), a cathode ( 16 ), and an active layer ( 14 ) provided between the anode and the cathode, the active layer contains a p-type semiconductor material having a band gap of 0.5 eV to 1.58 eV, and an n-type semiconductor material, the n-type semiconductor material is a C 60  fullerene derivative, and on an image obtained by binarizing an image of the active layer observed by a transmission electron microscope, the junction length between a phase of the n-type semiconductor material and a phase of the p-type semiconductor material is 120 μm to 170 μm per square micrometer of the area of the binarized image.

TECHNICAL FIELD

The present invention relates to a photoelectric conversion element such as a photodetector, and a method for producing the same.

BACKGROUND ART

For example, a photoelectric conversion element is a device that is highly useful from the viewpoint of energy saving and a reduction in the emission amount of carbon dioxide, and therefore attention is attracted to the photoelectric conversion element.

The photoelectric conversion element is an element comprising at least a pair of electrodes composed of an anode and a cathode, and an active layer provided between the pair of electrodes. In a photoelectric conversion element, one of electrodes is made of a transparent or semi-transparent material, and from a side of the electrode that is transparent or semi-transparent, light enters an organic active layer. By the energy (hν) of light that enters the organic active layer, charges (holes and electrons) are generated in the organic active layer, the generated holes move toward the anode, and the electrons move toward the cathode. The charges that have reached the anode and the cathode are extracted outside the element.

An active layer having a phase separation structure that is made by mixing an n-type semiconductor material (electron acceptor compound) and a p-type semiconductor material (electron donor compound) and comprises a phase containing the n-type semiconductor material and a phase containing the p-type semiconductor material is referred to as bulk heterojunction type active layer.

In the bulk heterojunction type active layer, the phase of the electron acceptor compound and the phase of the electron donor compound form a phase having a fine and complicated shape that is continuous from one electrode side to the other electrode side. The phases form a complicated interface with the phases separated from each other.

For improvement of the photoelectric conversion efficiency of a photoelectric conversion element comprising the bulk heterojunction type active layer, a configuration in which the area of pn junction between an n-type semiconductor and a p-type semiconductor is 100 μm² or more per cubic micrometer of the active layer has been known (see Patent Literature 1).

For improvement of the photoelectric conversion efficiency of a photoelectric conversion element comprising the bulk heterojunction active layer, for example, a configuration in which on an image obtained by binarizing an image of the active layer observed by a transmission electron microscope, the junction length between an electron donor compound and an electron acceptor compound is 100 μm or more per square micrometer of the area of the binarized image has been known (see Patent Literature 2).

RELATED ART DOCUMENTS Patent Literature

Patent Literature 1: JP 2010-41022 A

Patent Literature 2: JP 2011-238762 A

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

For example, a photoelectric conversion element is used as a photodetector. A photoelectric conversion element that is used as a photodetector is used with a voltage applied, and converts light entering the element and detects the light as a current. However, even when light does not enter, a weak current flows through the photoelectric conversion element. This current is known as a dark current, and causes a reduction in precision of light detection. In general, a dark current varies depending on a voltage applied to the photoelectric conversion element.

The voltage applied to the photoelectric conversion element varies depending on the type of device mounted on the element. Therefore, the dark current varies depending on the device mounted on the element. From the viewpoint of general purpose, it is preferable that the dark current does not vary depending on the device mounted. A reduction in variation of the dark current due to variation of the voltage applied to the photoelectric conversion element is required.

Means for Solving Problem

In order to solve the aforementioned problem, the present inventors have intensively studied, and as a result, found that when a band gap of a p-type semiconductor material and a junction length between a phase of the p-type semiconductor material and a phase of an n-type semiconductor material are adjusted, the aforementioned problem can be solved. Thus, the present invention has been completed. Specifically, the present invention provides the following [1] to [9].

[1] A photoelectric conversion element comprising:

-   -   an anode;     -   a cathode; and     -   an active layer provided between the anode and the cathode,         wherein     -   the active layer contains a p-type semiconductor material having         a band gap of 0.5 eV to 1.58 eV, and an n-type semiconductor         material,     -   the n-type semiconductor material is a C₆₀ fullerene derivative,         and     -   on an image obtained by binarizing an image of the active layer         observed by a transmission electron microscope, a junction         length between a phase of the n-type semiconductor material and         a phase of the p-type semiconductor material is 120 μm to 170 μm         per square micrometer of area of the binarized image.         [2] The photoelectric conversion element according to above [1],         wherein the p-type semiconductor material is a polymer compound         having a constitutional unit containing a thiophene skeleton.         [3] The photoelectric conversion element according to above [1]         or [2], wherein the C₆₀ fullerene derivative is C60PCBM.         [4] The photoelectric conversion element according to any one of         above [1] to [3], wherein the photoelectric conversion element         is a photodetector.         [5] An image sensor comprising the photoelectric conversion         element according to above [4].         [6] A fingerprint authentication device comprising the         photoelectric conversion element according to above [4].         [7] A method for producing a photoelectric conversion element         comprising an anode, a cathode, and an active layer provided         between the anode and the cathode, comprising:     -   forming the active layer comprising a step (i) of applying an         ink containing an n-type semiconductor material, a p-type         semiconductor material having a band gap of 0.5 eV to 1.58 eV,         and a solvent to a subject to be applied, to obtain a coating         film, and a step (ii) of removing the solvent from the coating         film, wherein     -   the n-type semiconductor material is a C₆₀ fullerene derivative,         and     -   on an image obtained by binarizing an image of the active layer         observed by a transmission electron microscope, a junction         length between the n-type semiconductor material and the p-type         semiconductor material is 120 μm to 170 μm per square micrometer         of area of the binarized image.         [8] The method for producing a photoelectric conversion element         according to above [7], wherein the p-type semiconductor         material is a polymer compound having a constitutional unit         containing a thiophene skeleton.         [9] The method for producing a photoelectric conversion element         according to above [7] or [8], wherein the C₆₀ fullerene         derivative is C60PCBM.

Effect of the Invention

According to the photoelectric conversion element of the present invention, variation of a dark current due to variation of a voltage applied to the photoelectric conversion element can be reduced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view schematically illustrating a cut end face of a photoelectric conversion element.

FIG. 2 is a view schematically illustrating a configuration example of an image detection portion.

FIG. 3 is a view schematically illustrating a configuration example of a fingerprint detection portion.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a photoelectric conversion element according to embodiments of the present invention will be described with reference to the drawings. The drawings only illustrate schematic shapes, sizes, and arrangements of constituent elements enough to understand the present invention. The present invention is not limited by the following description, and each constituent element can be appropriately changed without departing from the scope of the present invention. A configuration according to the embodiments of the present invention is not necessarily limited to the arrangements illustrated in the drawings during production or use.

[1. Photoelectric Conversion Element]

A photoelectric conversion element according to an embodiment is a photoelectric conversion element comprising an anode, a cathode, and an active layer provided between the anode and the cathode, wherein the active layer contains a p-type semiconductor material and an n-type semiconductor material, the n-type semiconductor material is a C₆₀ fullerene derivative, on an image obtained by binarizing an image of the active layer observed by a transmission electron microscope, the junction length between a phase of the p-type semiconductor material and a phase of the n-type semiconductor material is 120 μm to 170 μm per square micrometer of the area of the binarized image, and the band gap of the p-type semiconductor material is 0.5 eV to 1.58 eV, and specifically 0.50 eV to 1.58 eV.

Herein, an acceptable configuration example of the photoelectric conversion element of the present embodiment will be described. FIG. 1 is a view schematically illustrating a cut end face of the photoelectric conversion element of the embodiment.

As illustrated in FIG. 1, a photoelectric conversion element 10 of the embodiment is provided on a supporting substrate 11, for example. The photoelectric conversion element 10 comprises an anode 12 provided in contact with the supporting substrate 11, a hole transport layer 13 provided in contact with the anode 12, an active layer 14 provided in contact with the hole transport layer 13, an electron transport layer 15 provided in contact with the active layer 14, and a cathode 16 provided in contact with the electron transport layer 15. In the configuration example, the photoelectric conversion element further comprises a sealing substrate 17 provided in contact with the cathode 16.

(Substrate)

The photoelectric conversion element is generally formed on a substrate. On this substrate, an electrode including a cathode and an anode is generally formed. A material for the substrate is not particularly limited as long as it is a material that is not chemically changed during formation of a layer containing particularly an organic compound. Examples of the material for the substrate may include a glass, a plastic, a polymer film, and a silicone. When the substrate is an opaque substrate, it is preferable that an electrode on a side opposite to an electrode provided on a side of the opaque substrate (i.e., an electrode on a side away from the substrate) be a transparent or semi-transparent electrode.

(Electrode)

Examples of a material for the transparent or semi-transparent electrode may include a conductive metal oxide film and a semi-transparent metal thin film. Specific examples thereof may include conductive materials such as indium oxide, zinc oxide, tin oxide, and composites thereof including indium tin oxide (ITO), indium zinc oxide (IZO), and NESA, gold, platinum, silver, and copper. It is preferable that the material for the transparent or semi-transparent electrode be ITO, IZO, or tin oxide. For the electrode, a transparent conductive film formed from an organic compound such as a polyaniline or a derivative thereof or a polythiophene or a derivative thereof as a material may be used. The transparent or semi-transparent electrode may be an anode or a cathode.

When one of electrodes is transparent or semi-transparent, the other may be a low light transmitting electrode. Examples of a material for the low light transmitting electrode may include a metal and a conductive polymer. Specific examples of the material for the low light transmitting electrode may include metals such as lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, strontium, barium, aluminum, scandium, vanadium, zinc, yttrium, indium, cerium, samarium, europium, terbium, and ytterbium, alloys of two or more of the metals, alloys of one or more of the metals and one or more types of metal selected from the group consisting of gold, silver, copper, platinum, manganese, titanium, cobalt, nickel, tungsten, and tin, graphite, a graphite intercalation compound, a polyaniline and a derivative thereof, and a polythiophene and a derivative thereof. The alloys may include a magnesium-silver alloy, a magnesium-indium alloy, a magnesium-aluminum alloy, an indium-silver alloy, a lithium-aluminum alloy, a lithium-magnesium alloy, a lithium-indium alloy, and a calcium-aluminum alloy.

As a method for forming an electrode, any suitable and conventionally known formation method may be used. Examples of the method for forming an electrode may include a vacuum evaporation method, a sputtering method, an ion plating method, and a plating method.

(Active Layer)

The active layer contains a p-type semiconductor material (electron donor compound) and an n-type semiconductor material (electron acceptor compound). Details of suitable p-type semiconductor material and n-type semiconductor material will be described below. Whether a material is a p-type semiconductor material or an n-type semiconductor material can be relatively determined from HOMO and LUMO energy levels of a selected compound.

The thickness of the active layer is usually preferably 1 nm to 100 μm, and more preferably 2 nm to 1000 nm. For example, when the photoelectric conversion element is a solar cell, the thickness of the active layer is preferably 50 nm to 200 nm. For example, when the photoelectric conversion element is a photodetector, the thickness of the active layer is preferably 500 nm to 1000 nm.

On an image obtained by binarizing an image of an organic active layer observed by a transmission electron microscope, the junction length between a phase of the p-type semiconductor material and a phase of the n-type semiconductor material is 120 μm to 170 μm per square micrometer of the area of the binarized image.

A method for measuring the junction length between the phase of the p-type semiconductor material and the phase of the n-type semiconductor material may include a method in which the active layer is observed by a transmission electron microscope (TEM) and the length is measured. According to an image specific to elements contained in the p-type semiconductor material and the n-type semiconductor material, the phase of the p-type semiconductor material and the phase of the n-type semiconductor material can be observed to be separated. The image specific to the elements may include an elemental mapping image using an energy filter TEM, an energy loss image using an energy value that imparts the same contrast as that of an elemental mapping image, and an elemental mapping image obtained by energy dispersive X-ray analysis (STEM-EDX) using a scanning transmission electron microscope. An image is subjected to a binarization process in which the phase of the p-type semiconductor material is compared with the phase of the n-type semiconductor material, a bright phase is converted to white, and a dark phase is converted to black. Thus, the junction length between the phase of the p-type semiconductor material and the phase of the n-type semiconductor material can be calculated. Hereinafter, more specific description will be given.

The junction length can be calculated by a method including the following steps using computer hardware and software.

-   -   Step (i): A computer reads an obtained 20-eV loss image (TEM         image) using ImageJ (image processing software).     -   Step (ii): The computer convers the read image to a 16-bit         grayscale image using ImageJ.     -   Step (iii): The computer executes background correction of the         converted 16-bit grayscale image under a condition of a rolling         ball radius of 20 pixels.     -   Step (iv): The computer applies a median filter of 12 pixels to         the image subjected to the background correction.     -   Step (v): The computer executes binarization for the image         processed by the median filter using Otsu's method.     -   Step (vi): The computer extracts an interface on the image         binarized by processing with a command of Find Edge.     -   Step (vii): The computer calculates the area of the interface         extracted by processing with a command of Measure.     -   Step (viii): The computer divides the area of the obtained         interface by a length of one pixel to obtain a result as         “junction length.”     -   Step (ix): The computer divides the obtained junction length by         a visual field area to determine the junction length per unit         area.

The junction length between the phase of the p-type semiconductor material and the phase of the n-type semiconductor material is preferably 120 μm to 170 μm per square micrometer of the area of the binarized image.

In the photoelectric conversion element of the present invention, the band gap of the p-type semiconductor material in the active layer is a predetermined range, and the phase separation structure of the phase of the p-type semiconductor material and the phase of the n-type semiconductor material is a predetermined range. According to such a configuration, the specific dark current can be reduced.

Herein, a band gap (Eg) is a value (optical band gap) calculated by the following expression using the absorption edge wavelength of the p-type semiconductor material.

Band gap: Eg=hc/absorption edge wavelength (the Planck's constant: h=6.626×10⁻³⁴ Js, light velocity: c=3×10⁸ m/s)

Especially from the viewpoint of sensitivity in the photodetector, the lower limit value of the band gap of the p-type semiconductor material is preferably 0.5 eV or more, and specifically 0.50 eV or more. Especially from the viewpoint of conversion efficiency, it is more preferably 0.6 eV or more, and specifically 0.60 eV or more. From the viewpoint of optimization of absorption wavelength, the upper limit value of the band gap of the p-type semiconductor material is preferably 1.58 eV or less. Especially from the viewpoint of photoelectric conversion efficiency, it is more preferably 1.4 eV or less, and specifically 1.40 eV or less.

Herein, the specific dark current means a ratio between the magnitude of dark currents before and after changing an applied voltage. A small specific dark current means that even when a higher voltage is applied, an increase in leak current is small.

The specific dark current can be calculated, for example, as a ratio between the magnitude of dark currents at two different applied voltages. In general, when the applied voltage is high, the dark current is high. Therefore, the specific dark current can be calculated as a ratio of a dark current when the absolute value of applied voltage is higher and a dark current when the absolute value of applied voltage is lower. For example, the specific dark current can be calculated as a ratio of a dark current obtained during application of −5 V and a dark current obtained during application of −2 V (dark current during application of −5 V/dark current during application of −2 V).

The specific dark current is low, that is, the variation of dark current when the applied voltage (reverse bias voltage) is changed is small. Therefore, according to the photoelectric conversion element of the present invention, the sensitivity can be constantly stabilized regardless of high or low operating voltage.

(Interlayer)

As illustrated in FIG. 1, the photoelectric conversion element may include an additional interlayer such as a charge transport layer (electron transport layer, hole transport layer, electron injection layer, hole injection layer) as a further constituent element for improving properties such as photoelectric conversion efficiency.

As a material used for such an interlayer, any suitable and conventionally known material can be used. Examples of the material for the interlayer may include a halide and oxide of alkali metal or alkaline earth metal, such as lithium fluoride.

Examples of the material used for the interlayer may include fine particles of inorganic semiconductors such as titanium oxide, and a mixture of poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(4-styrene sulfonate) (PSS) (PEDOT: PSS).

As illustrated in FIG. 1, the photoelectric conversion element may include a hole transport layer between the anode and the active layer. The hole transport layer has a function of transporting holes from the active layer to the electrode.

The hole transport layer provided in contact with the anode may be especially referred to as hole injection layer. The hole transport layer (hole injection layer) provided in contact with the anode has a function of promoting injection of holes into the anode. The hole transport layer (hole injection layer) may be in contact with the active layer.

The hole transport layer contains a hole-transporting material. Examples of the hole-transporting material may include a polythiophene and a derivative thereof, an aromatic amine compound, a polymer compound containing a constitutional unit having an aromatic amine residue, CuSCN, CuI, NiO, and molybdenum oxide (MoO₃).

As illustrated in FIG. 1, the photoelectric conversion element may include an electron transport layer between the cathode and the active layer. The electron transport layer has a function of transporting electrons from the active layer to the cathode. The electron transport layer may be in contact with the cathode. The electron transport layer may be in contact with the active layer.

The electron transport layer contains an electron-transporting material. Examples of the electron-transporting material may include nanoparticles of zinc oxide, nanoparticles of gallium-doped zinc oxide, nanoparticles of aluminum-doped zinc oxide, polyethylenimine, polyethylenimine ethoxylated, and PFN-P2.

The interlayer can be formed by a coating method that is the same as that in the method for producing an active layer as described above.

(Use of Photoelectric Conversion Element)

Under irradiation with light, the photoelectric conversion element of the embodiment can generate a photovoltaic power between electrodes, and act as a solar cell. A plurality of solar cells that are integrated can be used as a thin film solar cell module.

When the photoelectric conversion element of the embodiment is irradiated with light from a side of a transparent or semi-transparent electrode with a voltage applied between electrodes, a photocurrent flows, and the photoelectric conversion element can act as a photodetector (photosensor). A plurality of photosensors that are integrated can be also used as an image sensor.

(Use Example of Photoelectric Conversion Element)

The photoelectric conversion element according to the embodiment of the present invention as described above can be suitably used for a detection portion provided in various electronic devices such as a workstation, a personal computer, a portable information terminal, an access management system, a digital camera, and a medical device.

The photoelectric conversion element (photodetector) of the present invention can be suitably used, for example, for an image detection portion (image sensor) for a solid imaging device such as an X-ray imaging device or a CMOS image sensor, a detection portion of detecting given characteristics of a part of a living body such as a fingerprint detection portion, a face detection portion, a vein detection portion, or an iris detection portion, or a detection portion of an optical biosensor such as a pulse oximeter, which is provided in the electronic device exemplified above.

Hereinafter, configuration examples of the image detection portion for a solid imaging device and a fingerprint detection portion for a biometric authorization device (fingerprint authentication device) among the detection portions for which the photoelectric conversion element according to the embodiment of the present invention can be suitably used will be described with reference to the drawings.

(Image Detection Portion)

FIG. 2 is a view schematically illustrating the configuration example of the image detection portion for a solid imaging device.

An image device portion 1 includes a CMOS transistor substrate 20, an interlayer insulating layer 30 provided so as to cover the CMOS transistor substrate 20, the photoelectric conversion element 10 according to the embodiment of the present invention that is provided on the interlayer insulating layer 30, an interlayer wiring portion 32 that is provided so as to pass through the interlayer insulating layer 30 and electrically connects the CMOS transistor substrate 20 to the photoelectric conversion element 10, a sealing layer 40 provided so as to cover the photoelectric conversion element 10, and a color filter 50 provided on the sealing layer 40.

The CMOS transistor substrate 20 has any suitable and conventionally known configuration in an aspect corresponding to a design.

The CMOS transistor substrate 20 includes a function element such as a CMOS transistor circuit (MOS transistor circuit) for achieving various functions, including a transistor, a capacitor, or the like that is formed within the thickness of the substrate.

Examples of the function element may include floating diffusion, a reset transistor, an output transistor, and a selection transistor.

In the CMOS transistor substrate 20, a signal reading circuit or the like is formed using such a function element, a wiring, and the like.

The interlayer insulating layer 30 can be made from any suitable and conventionally known insulating material such as silicon oxide or an insulating resin. For example, the interlayer wiring portion 32 can be made from any suitable and conventionally known conductive material (wiring material) such as copper or tungsten. For example, the interlayer wiring portion 32 may be a wiring inside a hole that is formed at the same time as formation of a wiring layer, or a buried plug formed separately from the wiring layer.

The sealing layer 40 can be made from any suitable and conventionally known material as long as penetration of harmful substance that may functionally deteriorate the photoelectric conversion element 10, such as oxygen or water, can be prevented or suppressed. The sealing layer 40 may be the sealing substrate 17 described above.

As the color filter 50, for example, a primary color filter that is made from any suitable and conventionally known material and corresponds to a design of the image device portion 1 can be used. As the color filter 50, a complementary color filter having a thickness smaller than that of the primary color filter can be used. As the complementary color filter, for example, a color filter in which three types of colors (yellow, cyan, magenta), (yellow, cyan, transparent), (yellow, transparent, magenta), or (transparent, cyan, magenta) are combined can be used. These color filters can be optionally and suitably arranged so as to correspond to a design of the photoelectric conversion element 10 and the CMOS transistor substrate 20 as long as a color image data can be produced.

Light received by the photoelectric conversion element 10 through the color filter 50 is converted to an electrical signal corresponding to the amount of light received by the photoelectric conversion element 10, and sent through the electrode outside the photoelectric conversion element 10 as a received signal, that is, an electrical signal corresponding to an imaging subject.

The received signal sent from the photoelectric conversion element 10 is then put through the interlayer wiring portion 32 into the CMOS transistor substrate 20, read by the signal reading circuit formed in the CMOS transistor substrate 20, and processed by any further, suitable, and conventionally known function portion that is not illustrated. Thus, an image data based on the imaging subject is produced.

(Fingerprint Detection Portion)

FIG. 3 is a view schematically illustrating the configuration example of the fingerprint detection portion.

A display device 2 of a portable information terminal includes a fingerprint detection portion 100 including the photoelectric conversion element 10 according to the embodiment of the present invention as a main constituent element, and a display panel portion 200 that is provided on the fingerprint detection portion 100 and displays a predetermined image.

In this configuration example, the fingerprint detection portion 100 is provided at a region that substantially matches a display region 200 a of the display panel portion 200. That is, the display panel portion 200 is integrally layered on the fingerprint detection portion 100.

When fingerprint detection is performed for only a part of the display region 200 a, the fingerprint detection portion 100 may be provided so as to correspond to only the part of the display region.

The fingerprint detection portion 100 includes the photoelectric conversion element 10 according to the embodiment of the present invention as a function portion that performs an essential function. The fingerprint detection element 100 may include any suitable and conventionally known member such as a protection film, a supporting substrate, a sealing substrate, a sealing member, a barrier film, a band-pass filter, or an infrared radiation-cutting filter, in an aspect corresponding to such a design that desired characteristics are obtained. For the fingerprint detection portion 100, a configuration of the image detection portion described can be utilized.

The photoelectric conversion element 10 may be included as any embodiment in the display region 200 a. For example, a plurality of photoelectric conversion elements 10 may be arranged in a matrix.

As described above, the photoelectric conversion element 10 is provided on the supporting substrate 11 or a sealing substrate, and an electrode (anode or cathode) is provided on the supporting substrate 11, for example, in a matrix.

Light received by the photoelectric conversion element 10 is converted to an electrical signal corresponding to the amount of light received by the photoelectric conversion element 10, and sent through the electrode outside the photoelectric conversion element 10 as a received signal, that is, an electrical signal corresponding to an imaged fingerprint.

In this configuration example, the display panel portion 200 is configured as an organic electroluminescent display panel (organic EL display panel) including a touch sensor panel. The display panel portion 200 may be configured, for example, as a display panel having any suitable and conventionally known configuration such as a liquid-crystal display panel including a light source such as a backlight, instead of the organic EL display panel.

The display panel portion 200 is provided on the fingerprint detection portion 100 described above. The display panel portion 200 includes an organic electroluminescent element (organic EL element) 220 as a function portion that performs an essential function. The display panel portion 200 may further include any suitable and conventionally known substrate such as a glass substrate (a supporting substrate 210 or a sealing substrate 240), and any suitable and conventionally known member such as a sealing member, a barrier film, a polarizing plate such as a circularly polarizing plate, or a touch sensor panel 230, in an embodiment corresponding to desired characteristics.

In the configuration example described above, the organic EL element 220 is used as a light source of a pixel in the display region 200 a, and further used as a light source for imaging a fingerprint in the fingerprint detection portion 100.

Herein, a motion of the fingerprint detection portion 100 will be simply described.

During execution of fingerprint authentication, the fingerprint detection portion 100 detects a fingerprint using light emitted from the organic EL element 220 of the display panel portion 200. Specifically, light emitted from the organic EL element 220 is sent through a constituent element provided between the organic EL element 220 and the photoelectric conversion element 10 of the fingerprint detection portion 100, and reflected from the skin of the fingertip (the surface of the finger) disposed in contact with the surface of the display panel portion 200 within the display region 200 a. At least a part of the light reflected from the surface of the finger is sent through the constituent element provided, received by the photoelectric conversion element 10, and converted to an electrical signal corresponding to the amount of light received of the photoelectric conversion element 10. From the converted electrical signal, image information about the fingerprint of the surface of the finger is made.

The portable information terminal including the display device 2 compares the obtained image information with fingerprint date for fingerprint authentication recorded in advance and executes fingerprint authentication at any suitable and conventionally known steps.

[2. Method for Producing Photoelectric Conversion Element]

A method for producing the photoelectric conversion element of the embodiment is not particularly limited. The photoelectric conversion element can be produced by a formation method suitable for a material selected for formation of each constituent element.

Since the active layer that is a main constituent element provided in the photoelectric conversion element of the embodiment is a bulk heterojunction type, the active layer can be produced by a coating method using an ink.

The method for producing a photoelectric conversion element is a method for producing a photoelectric conversion element comprising an anode, a cathode, and an active layer provided between the anode and the cathode, wherein a step of forming the active layer comprises a step (i) of applying an ink containing an n-type semiconductor material, a p-type semiconductor material having a band gap of 0.5 eV to 1.58 eV, and specifically 0.50 eV to 1.58 eV, and a solvent to a subject to be applied, to obtain a coating film, and a step (ii) of removing the solvent from the coating film, and on an image obtained by binarizing an image of the active layer observed by a transmission electron microscope, the junction length between a phase of the n-type semiconductor material and a phase of the p-type semiconductor material is 120 μm to 170 μm per square micrometer of the area of the binarized image.

Hereinafter, the steps (i) and (ii) included in the step of forming the active layer that is a main constituent element in the photoelectric conversion element of the present invention will be described.

(Step (i))

As a method for applying an ink to a subject to be applied, any suitable coating method can be used. The coating method is preferably a slit coating method, a blade coating method, a spin coating method, a microgravure-coating method, a gravure-coating method, a bar-coating method, an ink-jet printing method, a nozzle coating method, or a capillary coating method, more preferably a slit coating method, a spin coating method, a capillary coating method, or a bar-coating method, and further preferably a slit coating method or a spin coating method.

An ink for formation of the active layer is applied to a subject to be applied according to the photoelectric conversion element and the method for producing the same. The ink for formation of the active layer may be applied to a functional layer that is in the photoelectric conversion element and can form the active layer in a step of producing the photoelectric conversion element. Therefore, the subject coated with the ink for formation of the active layer varies depending on a layer structure of the photoelectric conversion element to be produced and an order of layer formation. For example, when the photoelectric conversion element has a layer structure of substrate/anode/hole transport layer/active layer/electron transport layer/cathode and a layer described on a more left side is formed early, the subject coated with the ink is a hole transport layer. For example, when the photoelectric conversion element has a layer structure of substrate/cathode/electron transport layer/active layer/hole transport layer/anode and a layer described on a more left side is formed early, the subject coated with the ink is an electron transport layer.

(Step (ii))

As a method for removing the solvent from the coating film of the ink, that is, a method for removing the solvent from the coating film to form a solidified film, any suitable method can be used. Examples of the method for removing the solvent may include drying methods such as a method that directly heating the solvent on a hot plate, a hot air drying method, a drying method by infrared radiation heating, a drying method by flash lamp annealing, and a drying method under reduced pressure.

The junction length between the phase of the p-type semiconductor material and the phase of the n-type semiconductor material can be adjusted by aspects (temperature, drying time) of the step (ii). For example, when the temperature is set to be lower and the drying time is set to be longer, the junction length tends to be increased. Therefore, when a drying condition is adjusted, the junction length can be optimized.

In addition to the steps (i) and (ii), the step of forming the active layer may include another step without impairing the object and effects of the present invention.

The method for producing a photoelectric conversion element may be a method for producing a photoelectric conversion element including a plurality of active layers or a method in which the steps (i) and (ii) are repeated a plurality of times.

(Ink)

The ink may be a solution or a dispersion liquid such as a dispersion liquid, an emulsion (emulsion liquid), or a suspension (suspension liquid). The ink of the embodiment is an ink for formation of the active layer, contains the p-type semiconductor material, the n-type semiconductor material, and a first solvent, and may desirably contain a second solvent. Hereinafter, a component for the ink will be described.

Herein, terms used commonly in the following description will be firstly described.

A “polymer compound” means a polymer that has a molecular weight distribution and a polystyrene-equivalent number average molecular weight of 1×10³ or more and 1×10⁸ or less. A constitutional unit included in the polymer compound is in total 100% by mole.

A “constitutional unit” means a unit of which the number present in the polymer compound is one or more.

A “hydrogen atom” may be a light hydrogen atom or a heavy hydrogen atom.

A “halogen atom” includes a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

“Optionally having a substituent” includes both embodiments where all hydrogen atoms constituting a compound or group are unsubstituted and a part or all of one or more hydrogen atoms are substituted with a substituent.

An “alkyl group” may be linear, branched, or cyclic unless otherwise specified. The number of carbon atoms of a linear alkyl group is usually 1 to 50, preferably 1 to 30, and more preferably 1 to 20, not including the number of carbon atoms of a substituent. The number of carbon atoms of a branched or cyclic alkyl group is usually 3 to 50, preferably 3 to 30, and more preferably 4 to 20, not including the number of carbon atoms of a substituent.

The alkyl group may have a substituent. Specific examples of the alkyl group may include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, an n-pentyl group, an isoamyl group, a 2-ethylbutyl group, an n-hexyl group, a cyclohexyl group, an n-heptyl group, a cyclohexylmethyl group, a cyclohexylethyl group, an n-octyl group, a 2-ethylhexyl group, a 3-n-propylheptyl group, an adamantyl group, an n-decyl group, a 3,7-dimethyloctyl group, a 2-ethyloctyl group, a 2-n-hexyl-decyl group, an n-dodecyl group, a tetradecyl group, a hexadecyl group, an octadecyl group, and an eicosyl group. Specific examples of an alkyl group having a substituent may include a trifluoromethyl group, a pentafluoroethyl group, a perfluorobutyl group, a perfluorohexyl group, a perfluorooctyl group, a 3-phenylpropyl group, a 3-(4-methylphenyl)propyl group, a 3-(3,5-di-n-hexylphenyl)propyl group, and a 6-ethyloxyhexyl group.

An “aryl group” means an atomic group derived by removal of a hydrogen atom directly bonded to a carbon atom constituting a ring from an aromatic hydrocarbon optionally having a substituent.

The aryl group may have a substituent. Specific examples of the aryl group may include a phenyl group, a 1-naphthyl group, a 2-naphthyl group, a 1-anthracenyl group, a 2-anthracenyl group, a 9-anthracenyl group, a 1-pyrenyl group, a 2-pyrenyl group, a 4-pyrenyl group, a 2-fluorenyl group, a 3-fluorenyl group, a 4-fluorenyl group, a 2-phenylphenyl group, a 3-phenylphenyl group, a 4-phenylphenyl group, and groups in which the groups have a substituent such as an alkyl group, an alkoxy group, an aryl group, or a fluorine atom.

An “alkoxy group” may be linear, branched, or cyclic. The number of carbon atoms of a linear alkoxy group is usually 1 to 40, and preferably 1 to 10, not including the number of carbon atoms of a substituent. The number of carbon atoms of a branched or cyclic alkoxy group is usually 3 to 40, and preferably 4 to 10, not including the number of carbon atoms of a substituent.

The alkoxy group may have a substituent. Specific examples of the alkoxy group may include a methoxy group, an ethoxy group, an n-propyloxy group, an isopropyloxy group, an n-butyloxy group, an isobutyloxy group, a tert-butyloxy group, an n-pentyloxy group, an n-hexyloxy group, a cyclohexyloxy group, an n-heptyloxy group, an n-octyloxy group, a 2-ethylhexyloxy group, an n-nonyloxy group, an n-decyloxy group, a 3,7-dimethyloctyloxy group, and a lauryloxy group.

The number of carbon atoms of an “aryloxy group” is usually 6 to 60, and preferably 6 to 48, not including the number of carbon atoms of a substituent.

The aryloxy group may have a substituent. Specific examples of the aryloxy group may include a phenoxy group, a 1-naphthyloxy group, a 2-naphthyloxy group, a 1-anthracenyloxy group, a 9-anthracenyloxy group, a 1-pyrenyloxy group, and groups in which the groups have a substituent such as an alkyl group, an alkoxy group, or a fluorine atom.

An “alkylthio group” may be linear, branched, or cyclic. The number of carbon atoms of a linear alkylthio group is usually 1 to 40, and preferably 1 to 10, not including the number of carbon atoms of a substituent. The number of carbon atoms of a branched or cyclic alkylthio group is usually 3 to 40, and preferably 4 to 10, not including the number of carbon atoms of a substituent.

The alkylthio group may have a substituent. Specific examples of the alkylthio group may include a methylthio group, an ethylthio group, a propylthio group, an isopropylthio group, a butylthio group, an isobutylthio group, a tert-butylthio group, a pentylthio group, a hexylthio group, a cyclohexylthio group, a heptylthio group, an octylthio group, a 2-ethylhexylthio group, a nonylthio group, a decylthio group, a 3,7-dimethyloctylthio group, a laurylthio group, and a trifluoromethylthio group.

The number of carbon atoms of an “arylthio group” is usually 6 to 60, and preferably 6 to 48, not including the number of carbon atoms of a substituent.

The arylthio group may have a substituent. Examples of the arylthio group may include a phenylthio group, a C1-C12 alkyloxyphenylthio group (“C1-C12” means that the number of carbon atoms of a group described after that is 1 to 12. Hereinafter as the same), a C1-C12 alkylphenylthio group, a 1-naphthylthio group, a 2-naphthylthio group, and a pentafluorophenylthio group.

A “p-valent heterocyclic group” (p is an integer of 1 or more) means an atomic group derived by removal of p hydrogen atoms among hydrogen atoms directly bonded to a carbon atom or a heteroatom constituting a ring from a heterocyclic compound optionally having a substituent. Among p-valent heterocyclic groups, a “p-valent aromatic heterocyclic group” is preferred. The “p-valent aromatic heterocyclic group” means an atomic group derived by removal of p hydrogen atoms among hydrogen atoms directly bonded to a carbon atom or a heteroatom constituting a ring from an aromatic heterocyclic compound optionally having a substituent.

Examples of a substituent may be in a heterocyclic compound may include a halogen atom, an alkyl group, an aryl group, an alkoxy group, an aryloxy group, an alkylthio group, an arylthio group, a monovalent heterocyclic group, a substituted amino group, an acyl group, an imine residue, an amido group, an acid imido group, a substituted oxycarbonyl group, an alkenyl group, an alkynyl group, a cyano group, and a nitro group.

The aromatic heterocyclic compound includes a compound in which an aromatic ring is fused with a heterocycle not exhibiting aromaticity in addition to a compound in which a heterocycle by itself exhibits aromaticity.

Specific examples of the compound in which a heterocycle exhibits aromaticity by itself among aromatic heterocyclic compounds may include oxadiazole, thiadiazole, thiazole, oxazole, thiophene, pyrrole, phosphol, furan, pyridine, pyrazine, pyrimidine, triazine, pyridazine, quinoline, isoquinoline, carbazole, and dibenzophosphol.

Specific examples of the compound in which an aromatic ring is fused with a heterocycle not exhibiting aromaticity among aromatic heterocyclic compounds may include phenoxazine, phenothiazine, dibenzoborole, dibenzosilole, and benzopyran.

The number of carbon atoms of a “monovalent heterocyclic group” is usually 2 to 60, and preferably 4 to 20, not including the number of carbon atoms of a substituent.

The monovalent heterocyclic group may have a substituent, and specific examples of the monovalent heterocyclic group may include a thienyl group, a pyrrolyl group, a furyl group, a pyridyl group, a piperidyl group, a quinolyl group, an isoquinolyl group, a pyrimidinyl group, a triazinyl group, and groups in which the groups have a substituent such as an alkyl group or an alkoxy group.

A “substituted amino group” means an amino group having a substituent. Examples of a substituent that may be in the substituted amino group may include an alkyl group, an aryl group, and a monovalent heterocyclic group. It is preferable that the substituent be an alkyl group, an aryl group, or a monovalent heterocyclic group. The number of carbon atoms of the substituted amino group is usually 2 to 30.

Examples of the substituted amino group may include dialkylamino groups such as a dimethylamino group and a diethylamino group, and diarylamino groups such as a diphenylamino group, a bis(4-methylphenyl)amino group, a bis(4-tert-butylphenyl)amino group, and a bis(3,5-di-tert-butylphenyl)amino group.

The number of carbon atoms of an “acyl group” is usually about 2 to 20, and preferably 2 to 18. Specific examples of the acyl group may include an acetyl group, a propionyl group, a butyryl group, an isobutyryl group, a pivaloyl group, a benzoyl group, a trifluoroacetyl group, and a pentafluorobenzoyl group.

An “imine residue” means an atomic group derived by removal of a hydrogen atom directly bonded to a carbon atom or a nitrogen atom constituting a carbon atom-nitrogen atom double bond from an imine compound. The “imine compound” means an organic compound having a carbon atom-nitrogen atom double bond in the molecule. Examples of the imine compound may include an aldimine, a ketimine, and a compound in which a hydrogen atom bonded to a nitrogen atom constituting a carbon atom-nitrogen atom double bond in an aldimine is substituted with an alkyl group or the like.

The number of carbon atoms of the imine residue is usually about 2 to 20, and preferably 2 to 18. Examples of the imine residue may include groups represented by the following structural formulae.

An “amido group” means an atomic group derived by removal of a hydrogen atom bonded to a nitrogen atom from an amide. The number of carbon atoms of the amido group is usually 1 to 20, and preferably 1 to 18. Specific examples of the amido group may include a formamido group, an acetamido group, a propioamido group, a butyramido group, a benzamido group, a trifluoroacetamido group, a pentafluorobenzamido group, a diformamido group, a diacetamido group, a dipropioamido group, a dibutyramido group, a dibenzamido group, a ditrifuloroacetamido group, and a dipentafluorobenzamido group.

An “acid imido group” means an atomic group derived by removal of a hydrogen atom bonded to a nitrogen atom from an acid imide. The number of carbon atoms of the acid imido group is usually 4 to 20. Specific examples of the acid imido group may include groups represented by the following structural formulae.

A “substituted oxycarbonyl group” means a group represented by R′—O—(C═O)—. Herein, R′ is an alkyl group, an aryl group, an arylalkyl group, or a monovalent heterocyclic group.

The number of carbon atoms of the substituted oxycarbonyl group is usually about 2 to 60, and preferably 2 to 48.

Specific examples of the substituted oxycarbonyl group may include a methoxycarbonyl group, an ethoxycarbonyl group, a propoxycarbonyl group, an isopropoxycarbonyl group, a butoxycarbonyl group, an isobutoxycarbonyl group, a tert-butoxycarbonyl group, a pentyloxycarbonyl group, a hexyloxycarbonyl group, a cyclohexyloxycarbonyl group, a heptyloxycarbonyl group, an octyloxycarbonyl group, a 2-ethylhexyloxycarbonyl group, a nonyloxycarbonyl group, a decyloxycarbonyl group, a 3,7-dimethyloctyloxycarbonyl group, a dodecyloxycarbonyl group, a trifluoromethoxycarbonyl group, a pentafluoroethoxycarbonyl group, a perfluorobutoxycarbonyl group, a perfluorohexyloxycarbonyl group, a perfluorooctyloxycarbonyl group, a phenoxycarbonyl group, a naphthoxycarbonyl group, and a pyridyloxycarbonyl group.

An “alkenyl group” may be linear, branched, or cyclic. The number of carbon atoms of a linear alkenyl group is usually 2 to 30, and preferably 3 to 20, not including the number of carbon atoms of a substituent. The number of carbon atoms of a branched or cyclic alkenyl group is usually 3 to 30, and preferably 4 to 20, not including the number of carbon atoms of a substituent.

The alkenyl group may have a substituent. Specific examples of the alkenyl group may include a vinyl group, a 1-propenyl group, a 2-propenyl group, a 2-butenyl group, a 3-butenyl group, a 3-pentenyl group, a 4-pentenyl group, a 1-hexenyl group, a 5-hexenyl group, a 7-octenyl group, and groups in which the groups have a substituent such as an alkyl group or an alkoxy group.

An “alkynyl group” may be linear, branched, or cyclic. The number of carbon atoms of a linear alkenyl group is usually 2 to 20, and preferably 3 to 20, not including the number of carbon atoms of a substituent. The number of carbon atoms of a branched or cyclic alkenyl group is usually 4 to 30, and preferably 4 to 20, not including the number of carbon atoms of a substituent.

The alkynyl group may have a substituent. Specific examples of the alkynyl group may include an ethynyl group, a 1-propynyl group, a 2-propynyl group, a 2-butynyl group, a 3-butynyl group, a 3-pentynyl group, a 4-pentynyl group, a 1-hexynyl group, a 5-hexynyl group, and groups in which the groups have a substituent such as an alkyl group or an alkoxy group.

(P-type Semiconductor Material)

The p-type semiconductor material may be a low molecular compound or a polymer compound.

Examples of the p-type semiconductor material that is a low molecular compound may include a phthalocyanine, a metal phthalocyanine, a porphyrin, a metal porphyrin, an oligothiophene, a tetracene, a pentacene, and a rubrene.

When the p-type semiconductor material is a polymer compound, the polymer compound has a predetermined polystyrene-equivalent weight average molecular weight.

Herein, the polystyrene-equivalent weight average molecular weight means a weight average molecular weight calculated by gel permeation chromatography (GPC) using a standard sample of polystyrene.

From the viewpoint of solubility in the solvent, the polystyrene-equivalent weight average molecular weight of the p-type semiconductor material is preferably 20,000 or more and 200,000 or less, more preferably 30,000 or more and 180,000 or less, and further preferably 40,000 or more and 150,000 or less.

Examples of the p-type semiconductor material that is a polymer compound may include a polyvinyl carbazole and a derivative thereof, a polysilane and a derivative thereof, a polysiloxane having an aromatic amine structure in a side chain or a main chain, a polyaniline and a derivative thereof, a polythiophene and a derivative thereof, a polypyrrole and a derivative thereof, a polyphenylenevinylene and a derivative thereof, a polythienylenevinylene and a derivative thereof, and a polyfluorene and a derivative thereof.

From the viewpoint of a reduction in specific dark current, it is preferable that the p-type semiconductor material that is a polymer compound be a polymer compound having a constitutional unit containing a thiophene skeleton.

It is preferable that the p-type semiconductor material is a polymer compound having a constitutional unit represented by the following Formula (I) and/or a constitutional unit represented by the following Formula (II).

In Formula (I), Ar¹ and Ar² are a trivalent aromatic heterocyclic group, and Z is each of groups represented by the following Formulae (Z-1) to (Z-7).

[Chemical Formula 4]

—Ar³—  (II)

In Formula (II), Ar³ is a divalent aromatic heterocyclic group.

In Formulae (Z-1) to (Z-7), R is a hydrogen atom, a halogen atom, an alkyl group, an aryl group, an alkoxy group, an aryloxy group, an alkylthio group, an arylthio group, a monovalent heterocyclic group, a substituted amino group, an acyl group, an imine residue, an amido group, an acid imido group, a substituted oxycarbonyl group, an alkenyl group, an alkynyl group, a cyano group, or a nitro group. When each of Formulae (Z-1) to (Z-7) has two Rs, the two Rs may be the same as or different from each other.

It is preferable that the constitutional unit represented by Formula (I) is a constitutional unit represented by the following Formula (I-1).

In Formula (I-1), Z has the same meaning as described above.

Examples of the constitutional unit represented by Formula (I-1) may include constitutional units represented by the following Formulae (501) to (505).

In Formulae (501) to (505), R has the same meaning as described above. When there are two Rs, the two Rs may be the same as or different from each other.

The number of carbon atoms of the divalent aromatic heterocyclic group represented by Ar³ is usually 2 to 60, preferably 4 to 60, and more preferably 4 to 20. The divalent aromatic heterocyclic group represented by Ar³ may have a substituent. Examples of the substituent that may be in the divalent aromatic heterocyclic group represented by Ar³ may include a halogen atom, an alkyl group, an aryl group, an alkoxy group, an aryloxy group, an alkylthio group, an arylthio group, a monovalent heterocyclic group, a substituted amino group, an acyl group, an imine residue, an amido group, an acid imido group, a substituted oxycarbonyl group, an alkenyl group, an alkynyl group, a cyano group, and a nitro group.

Examples of the divalent aromatic heterocyclic group represented by Ar³ may include groups represented by the following Formulae (101) to (185).

In Formulae (101) to (185), R has the same meaning as described above. When there are a plurality of Rs, the Rs may be the same as or different from each other.

It is preferable that the constitutional unit represented by Formula (II) be each of constitutional units represented by the following Formulae (II-1) to (II-6).

In Formulae (II-1) to (II-6), X¹ and X² are each independently an oxygen atom or a sulfur atom, and R has the same meaning as described above. When there are a plurality of Rs, the Rs may be the same as or different from each other.

From the viewpoint of availability of raw material compounds, it is preferable that all X¹ and X² in Formulae (II-1) to (II-6) be a sulfur atom.

It is preferable that the p-type semiconductor material be a polymer compound having a constitutional unit containing a thiophene skeleton.

The polymer compound that is the p-type semiconductor material may contain constitutional units represented by two or more types of Formula (I), or contain constitutional units represented by two or more types of Formula (II).

In order to improve the solubility in the solvent, the polymer compound that is the p-type semiconductor material may contain a constitutional unit represented by the following Formula (III).

[Chemical Formula 13]

—Ar⁴—  (III)

In Formula (III), Ar⁴ is an arylene group.

The arylene group represented by Ar⁴ means an atomic group derived by removal of two hydrogen atoms from an aromatic hydrocarbon optionally having a substituent. The aromatic hydrocarbon also contains a compound having a fused ring and a compound in which two or more rings selected from the group consisting of an independent benzene ring and a fused ring are bonded directly or via a divalent group such as a vinylene group.

Examples of a substituent that may be in the aromatic hydrocarbon may include substituents that are the same as those exemplified as the substituent that may be in the heterocyclic compound.

The number of carbon atoms of the arylene group except for the substituent is usually 6 to 60, and preferably 6 to 20. The number of carbon atoms of the arylene group including the substituent is usually 6 to 100.

Examples of the arylene group may include a phenylene group (e.g., the following Formulae 1 to 3), a naphthalene-diyl group (e.g., the following Formulae 4 to 13), an anthracene-diyl group (e.g., the following Formulae 14 to 19), a biphenyl-diyl group (e.g., the following Formulae 20 to 25), a terphenyl-diyl group (e.g., the following Formulae 26 to 28), a fused ring compound group (e.g., the following Formulae 29 to 35), a fluorene-diyl group (e.g., the following Formulae 36 to 38), and a benzofluorene-diyl group (e.g., the following Formulae 39 to 46).

In Formulae 1 to 46, R that is the substituent has the same meaning as described above. When there are a plurality of Rs, the Rs may be the same as or different from each other.

The constitutional unit constituting the polymer compound that is the p-type semiconductor material may be a constitutional unit in which two or more constitutional units that are two or more types selected from the constitutional unit represented by Formula (I), the constitutional unit represented by Formula (II), and the constitutional unit represented by Formula (III) are connected in combination.

When the polymer compound that is the p-type semiconductor material contains the constitutional unit represented by Formula (I) and/or the constitutional unit represented by Formula (II), the total amount of the constitutional unit represented by Formula (I) and the constitutional unit represented by Formula (II) is usually 20 to 100% by mole relative to an amount of all constitutional units contained in the polymer compound of 100% by mole. The total amount is preferably 40 to 100% by mole, and more preferably 50 to 100% by mole since the charge transportation as the p-type semiconductor material is improved.

Specific examples of the polymer compound that is the p-type semiconductor material may include polymer compounds represented by the following Formulae P-1 to P-6.

The ink may contain only one type of the p-type semiconductor material, or a combination of two or more types of the p-type semiconductor materials at an optional ratio.

(N-type Semiconductor Material)

From the viewpoint of a reduction in specific dark current, it is preferable that the n-type semiconductor material be a C₆₀ fullerene derivative. The C₆₀ fullerene derivative means a compound in which at least a part of C₆₀ fullerene is modified.

Examples of the C₆₀ fullerene derivative may include compounds represented by the following Formulae (N-1) and (N-2).

In Formulae (N-1) and (N-2), R^(a) is an alkyl group, an aryl group, a monovalent heterocyclic group, or a group having an ester structure. A plurality of R^(a)s may be the same as or different from each other.

R^(b) is an alkyl group or an aryl group. A plurality of R^(b)s may be the same as or different from each other.

Examples of the group having an ester structure represented by R^(a) may include a group represented by the following Formula (19).

In Formula (19), u1 is an integer of 1 to 6. u2 is an integer of 0 to 6. R^(c) is an alkyl group, an aryl group, or a monovalent heterocyclic group.

Examples of the C₆₀ fullerene derivative may include the following compounds.

Specific examples of the C₆₀ fullerene derivative may include [6,6]-phenyl-C61 butyric acid methyl ester (C60PCBM), and [6,6]-thienyl-C61 butyric acid methyl ester.

The ink may contain only one type of the n-type semiconductor material, or a combination of two or more types of the n-type semiconductor materials at an optional ratio.

(Ratio by Weight (P/N Ratio) of P-type Semiconductor Material and N-type Semiconductor Material)

The ratio by weight (p-type semiconductor material/n-type semiconductor material) of the p-type semiconductor material and the n-type semiconductor material in the ink is preferably within a range of 9/1 to 1/9, more preferably within a range of 2/1 to 1/9, and further preferably within a range of 1/1 to 1/9. From the viewpoint of making the junction length between the phase of the p-type semiconductor material and the phase of the n-type semiconductor material within a suitable range when the photoelectric conversion element is especially a photodetector, the ratio by weight is particularly preferably within a range of 1/1 to 1/3. The p/n ratio can be used as an indication for adjustment of junction length between the phase of the p-type semiconductor material and the phase of the n-type semiconductor material.

(First Solvent)

The solvent may be selected in consideration of solubility of the selected p-type semiconductor material and n-type semiconductor material and properties (boiling point, etc.) corresponding to a drying condition during formation of the active layer.

The first solvent that is a main solvent is an aromatic hydrocarbon (hereinafter simply referred to as aromatic hydrocarbon) optionally having a substituent (alkyl group or halogen atom). It is preferable that the first solvent be selected in consideration of the solubility of the selected p-type semiconductor material and n-type semiconductor material.

Examples of such an aromatic hydrocarbon may include toluene, xylene (e.g., o-xylene, m-xylene, and p-xylene), trimethylbenzene (e.g., mesitylene and 1,2,4-trimethylbenzene (pseudocumene)), butylbenzene (e.g., n-butylbenzene, sec-butylbenzene, and tert-butylbenzene), methylnaphthalene (e.g., 1-methylnaphthalene), tetralin, indan, chlorobenzene, and dichlorobenzene (o-dichlorobenzene).

The first solvent may include only one type of the aromatic hydrocarbon or two or more types of the aromatic hydrocarbons. It is preferable that the first solvent include only one type of the aromatic hydrocarbon.

It is preferable that the first solvent contain one or more types selected from the group consisting of toluene, o-xylene, m-xylene, p-xylene, mesitylene, pseudocumene, n-butylbenzene, sec-butylbenzene, tert-butylbenzene, methylnaphthalene, tetralin, indane, chlorobenzene, and o-dichlorobenzene, and it is more preferable that the first solvent contain pseudocumene, chlorobenzene, or o-dichlorobenzene.

(Second Solvent)

It is preferable that the second solvent be a solvent especially selected from the viewpoint of enhancing the solubility of the n-type semiconductor material and making the junction length between the phase of the n-type semiconductor material and the phase of the p-type semiconductor material in the active layer suitable. Examples of the second solvent may include ketone solvents such as acetone, methyl ethyl ketone, cyclohexanone, acetophenone, and propiophenone, and ester solvents such as ethyl acetate, butyl acetate, phenyl acetate, ethyl cellosolve acetate, methyl benzoate, butyl benzoate, and benzyl benzoate.

From the viewpoint of a reduction in specific dark current, it is preferable that the second solvent be propiophenone or benzyl benzoate.

(Combination of First Solvent with Second Solvent)

Examples of combination of the first solvent with the second solvent may include combinations shown in the Table 1 below.

TABLE 1 First solvent Second solvent pseudocumene propiophenone

(Ratio by Weight of First Solvent and Second Solvent)

From the viewpoint of improving the solubility of the p-type semiconductor material and the n-type semiconductor material, it is preferable that the ratio by weight (first solvent/second solvent) of the first solvent that is a main solvent to the second solvent that is an added solvent be within a range of 85/15 to 99/1.

(Total Percentage by Weight of First Solvent and Second Solvent in Ink)

From the viewpoint of improving the solubility of the p-type semiconductor material and the n-type semiconductor material, the total weight of the first solvent and the second solvent in the ink is preferably 90% by weight or more, more preferably 92% by weight or more, and further preferably 95% by weight or more when the total weight of the ink is 100% by weight. From the viewpoint of increasing the concentrations of the p-type semiconductor material and the n-type semiconductor material in the ink and facilitating formation of a film having equal to or more than predetermined thickness, it is preferably 99% by weight or less, more preferably 98% by weight or less, and further preferably 97.5% by weight or less.

(Optional Solvent)

The ink may contain an optional solvent other than the first solvent and the second solvent. When the total weight of all the solvents in the ink is 100% by weight, the content of the optional solvent is preferably 5% by weight or less, more preferably 3% by weight or less, and further preferably 1% by weight or less. It is preferable that the optional solvent be a solvent having a boiling point higher than that of the second solvent.

(Optional Component)

In addition to the first solvent, the second solvent, the p-type semiconductor material, and the n-type semiconductor material, the ink may contain optional components such as an ultraviolet light absorber, an antioxidant, a sensitizer for sensitizing a function of generating a charge by absorbed light, and a light stabilizer for enhancing stability to ultraviolet light without impairing the objects and effects of the present invention.

(Concentration of P-type Semiconductor Material and N-type Semiconductor Material in Ink)

The total concentration of the p-type semiconductor material and the n-type semiconductor material in the ink is preferably 0.01% by weight or more and 20% by weight or less, more preferably 0.01% by weight or more and 10% by weight or less, further preferably 0.01% by weight or more and 5% by weight or less, and particularly preferably 0.1% by weight or more and 5% by weight or less. In the ink, the p-type semiconductor material and the n-type semiconductor material may be dissolved or dispersed. It is preferable that at least a part of the p-type semiconductor material and the n-type semiconductor material be dissolved, and it is more preferable that all the p-type semiconductor material and the n-type semiconductor material be dissolved.

(Preparation of Ink)

The ink can be prepared by a known method. For example, the ink can be prepared by a method in which the first solvent and the second solvent are mixed to prepare a mixed solvent, and the p-type semiconductor material and the n-type semiconductor material are added to the mixed solvent, a method in which the p-type semiconductor material is added to the first solvent, the n-type semiconductor material is added to the second solvent, and the first solvent and the second solvent that contain each of the materials are mixed, or the like.

The first solvent and the second solvent and the p-type semiconductor material and the n-type semiconductor material may be mixed with heating at a temperature equal to or lower than the boiling points of the solvents.

The first solvent and the second solvent and the p-type semiconductor material and the n-type semiconductor material are mixed, and the obtained mixture is filtered through a filter. Thus, the obtained filtrate may be used as the ink. As the filter, for example, a filter made of a fluorine resin such as polytetrafluoroethylene (PTFE) can be used.

EXAMPLES

Hereinafter, Examples will be shown to describe the present invention in more details. The present invention is not limited to Examples described below.

In Examples, a p-type semiconductor material (electron donor compound) illustrated in Table 2 and an n-type semiconductor material (electron acceptor compound) illustrated in Table 2 were used.

TABLE 2 Bandgap Number (eV) Chemical structure p-type semiconductor material P-1 1.38

(25:25:50;mol %) P-2 1.24

P-3 1.18

(25:25:50;mol %) P-4 1.59

(50:50;mol %) P-5 1.80

P-6 2.10

(50:50;mol %)

TABLE 3 Num- ber Chemical structure N-type semi- con- ductor material N-1′

N-3

A polymer compound P-1 that was a p-type semiconductor material was synthesized with reference to a method described in WO2013/051676, and used.

As a polymer compound P-2 that was a p-type semiconductor material, PDPP3T (trade name, available from Lumtec) was commercially obtained and used.

A polymer compound P-3 that was a p-type semiconductor material was synthesized with reference to a method described in WO2011/052709, and used.

As a polymer compound P-4 that was a p-type semiconductor material, PCE10 (trade name, available from 1-material) was commercially obtained and used.

As a polymer compound P-5 that was a p-type semiconductor material, PDTSTPD (trade name, available from 1-material) was commercially obtained and used.

A polymer compound P-6 that was a p-type semiconductor material was synthesized with reference to a method described in JP 2010-74127 A, and used.

As a compound N-1′ that was an n-type semiconductor material, E100 (trade name, available from Frontier Carbon Corporation) was commercially obtained and used.

As a compound N-3 that was an n-type semiconductor material, ADS71BFA (trade name, available from American dye source, Inc.) was commercially obtained and used.

Solvents used in Examples and boiling points thereof (° C.) are shown in Table 4.

TABLE 4 Boiling point Solvent (° C.) pseudocumene 169 2-methylquinoline 247 propiophenone 208 benzylbenzoate 323 tetralin 206 o-xylene 145 acetophenone 202 chlorobenzene 131 o-dichlorobenzene 181

Preparative Example 1 (Preparation of Ink)

A mixed solvent was prepared by using pseudocumene as a first solvent and propiophenone as a second solvent at a ratio by weight of the first solvent to the second solvent of 95:5. In the prepared mixed solvent, the polymer compound P-1 that was a p-type semiconductor material and the compound N-1′ that was an n-type semiconductor material were mixed so that the concentration of the p-type semiconductor material in the total weight of an ink was 1% by weight and the concentration of the n-type semiconductor material in the total weight of the ink was 2.5% by weight (p-type semiconductor material/n-type semiconductor material=1/2.5 (hereinafter referred to as p/n ratio)), and stirred at 80° C. for 12 hours. The obtained mixed solution was then filtered through a PTFE filter having a pore diameter of 5 μm, to obtain an ink (I-1).

Preparative Examples 2 to 3 and Comparative Preparative Examples 1 to 5

Inks (I-2) to (I-3) and (C-1) to (C-5) were each prepared in the same manner as in Preparative Example 1 by using a first solvent and a second solvent as a mixed solvent in a combination at a mixing ratio (% by weight) shown in Table 5-1 or a single solvent, a polymer compound P-1 (1% by weight as a whole composition, the weight average molecular weight (Mw) is shown together) that was a p-type semiconductor material, and a compound N-1′ or N-3 that was an n-type semiconductor material.

Preparative Examples 4 and 5 and Comparative Preparative Example 6

Inks (I-4) to (I-5) and (C-6) were each prepared in the same manner as in Preparative Example 1 by using a first solvent and a second solvent as a mixed solvent in a combination at a mixing ratio (% by weight) shown in Table 5-1 or a single solvent, a polymer compound P-2 (1% by weight as a whole composition, the weight average molecular weight (Mw) is shown together) that was a p-type semiconductor material, and a compound N-1′ that was an n-type semiconductor material.

Preparative Examples 6 to 8

Inks (I-6) to (I-8) were each prepared in the same manner as in Preparative Example 1 by using a first solvent and a second solvent as a mixed solvent in a combination at a mixing ratio (% by weight) shown in Table 5-1 or a single solvent, a polymer compound P-3 (1% by weight as a whole composition, the weight average molecular weight (Mw) is shown together) that was a p-type semiconductor material, and a compound N-1′ that was an n-type semiconductor material.

Preparative Examples 7 to 8

Inks (C-7) to (C-8) were each prepared in the same manner as in Preparative Example 1 by using a first solvent and a second solvent as a mixed solvent in a combination at a mixing ratio (% by weight) shown in Table 5-1, a polymer compound P-4 (1% by weight as a whole composition, the weight average molecular weight (Mw) is shown together) that was a p-type semiconductor material, and a compound N-1′ that was an n-type semiconductor material.

Comparative Preparative Examples 9 to 12

Inks (C-9) to (C-12) were each prepared in the same manner as in Preparative Example 1 by using a first solvent and a second solvent as a mixed solvent in a combination at a mixing ratio (% by weight) shown in Table 5-1 or 5-2 or a single solvent, a polymer compound P-5 (1% by weight as a whole composition, the weight average molecular weight (Mw) is shown together) that was a p-type semiconductor material, and a compound N-1′ that was an n-type semiconductor material.

Comparative Preparative Examples 13 to 16

Inks (C-13) to (C-16) were each prepared in the same manner as in Preparative Example 1 by using a first solvent and a second solvent as a mixed solvent in a combination at a mixing ratio (% by weight) shown in Table 5-2, a polymer compound P-6 (1% by weight as a whole composition, the weight average molecular weight (Mw) is shown together) that was a p-type semiconductor material, and a compound N-1′ that was an n-type semiconductor material.

TABLE 5-1 Molecular Mixing ratio weight of (First solvent/ p-type semi- p-type semi- n-type semi- First Second Second solvent) conductor conductor conductor Ink solvent solvent (% by weight) material material (Mw) material p/n ratio Preparative I-1 pseudocumene propiophenone 95/5  P-1 62,200 N-1′ 1/2.5 example 1 Preparative I-2 chlorobenzene — — P-1 39,600 N-1′ 1/3  example 2 Preparative I-3 o-dichlorobenzene — — P-1 78,900 N-1′ 1/1.5 example 3 Preparative I-4 pseudocumene benzylbenzoate 95/5  P-2 59,800 N-1′ 1/1  example 4 Preparative I-5 pseudocumene propiophenone 90/10 P-2 59,800 N-1′ 1/2  example 5 Preparative I-6 pseudocumene benzylbenzoate 90/10 P-3 59,800 N-1′ 1/2  example 6 Preparative I-7 o-dichlorobenzene — 90/10 P-3 59,800 N-1′ 1/2  example 7 Preparative I-8 pseudocumene propiophenone 90/10 P-3 59,800 N-1′ 1/2  example 8 Comparative C-1 pseudocumene propiophenone 95/5  P-1 62,200 N-1′ 1/1  preparative example 1 Comparative C-2 pseudocumene propiophenone 95/5  P-1 78,900 N-1′ 1/1  preparative example 2 Comparative C-3 pseudocumene propiophenone 95/5  P-1 62,200 N-3 1/2.5 preparative example 3 Comparative C-4 o-dichlorobenzene — — P-1 78,900 N-3 1/1.5 preparative example 4 Comparative C-5 o-xylene acetophenone 90/10 P-1 78,900 N-3 1/1.5 preparative example 5 Comparative C-6 tetralin — — P-2 59,800 N-1′ 1/2  preparative example 6 Comparative C-7 pseudocumene propiophenone 90/10 P-4 204,800 N-1′ 1/1.5 preparative example 7 Comparative C-8 pseudocumene 2-methylquinoline 90/10 P-4 39,000 N-1′ 1/1.5 preparative example 8 Comparative C-9 o-dichlorobenzene — — P-5 45,000 N-1 1/1.5 preparative example 9 Comparative C-10 pseudocumene benzylbenzoate 90/10 P-5 45,000 N-1′ 1/1.5 preparative example 10

TABLE 5-2 Comparative C-11 pseudocumene propiophenone 90/10 P-5 45,000 N-1′ 1/1.5 preparative example 11 Comparative C-12 tetralin — — P-5 45,000 N-1′ 1/1.5 preparative example 12 Comparative C-13 pseudocumene propiophenone — P-6 36,900 N-1′ 1/1.5 preparative example 13 Comparative C-14 o-xylene acetophenone 90/10 P-6 36,900 N-1′ 1/1.5 preparative example 14 Comparative C-15 pseudocumene 2-methylquinoline 90/10 P-6 36,900 N-1′ 1/1.5 preparative example 15 Comparative C-16 pseudocumene benzylbenzoate 90/10 P-6 36,900 N-1′ 1/1.5 preparative example 16

Example 1 (Preparation and Evaluation of Photoelectric Conversion Element)

A glass substrate on which a thin film (anode) of ITO with a thickness of 150 nm was formed by a sputtering method was prepared, and subjected to an ozone UV treatment as a surface treatment.

A suspension in which poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid (PEDOT/PSS) were dissolved in water (Clevios P VP AI4083, available from Heraeus) was then filtered through a filter having a pore diameter of 0.45 μm. The suspension after the filtration was applied to the thin film of ITO of the substrate at a thickness of 40 nm by a spin coating method to form a coating film.

Subsequently, the glass substrate having the coating film was dried in air on a hot plate at 200° C. for 10 minutes, to form a hole transport layer.

The ink composition (I-1) was then applied to the formed hole transport layer by a spin coating method, and dried on a hot plate heated to 70° C., to form an active layer. The active layer formed had a thickness of approximately 100 nm.

Next, a 45% by weight dispersion liquid of zinc oxide nanoparticles (particle diameter: 20 to 30 nm) in isopropanol (2-propanol) (HTD-711Z, available from Tayca Corporation) was diluted with 3-pentanol in an amount of 10-fold parts by weight of the isopropanol dispersion liquid, to prepare a coating liquid. The obtained coating liquid was applied to the active layer by a spin coating method, and the glass substrate having the coating film was dried under a nitrogen gas atmosphere to form an electron transport layer having a thickness of approximately 40 nm.

Subsequently, an Ag layer having a thickness of approximately 80 nm was formed on the active layer as an electrode (cathode) in a resistive heating vapor deposition apparatus.

Next, a UV-curing sealant was applied to the periphery of a layered body, bonded to the glass substrate, and irradiated with UV light. The layered body was sealed to obtain a photoelectric conversion element. The planar shape as viewed in a thickness direction of the obtained photoelectric conversion element was a 1 cm×1 cm square.

A dark current was measured using the obtained photoelectric conversion element. In the measurement of a dark current, a semiconductor parameter analyzer (Agilent technology B1500A, manufactured by Agilent Technologies) was used. Values of dark current were obtained during application of −5 V and −2 V. Based on the obtained values of dark current, a dark current ratio was calculated. The dark current ratio herein means a ratio of the obtained dark current during application of −5 V and the obtained dark current during application of −2 V. The results are shown in Table 6.

A band gap (Eg) was calculated by the following expression using the absorption edge wavelength of the p-type semiconductor material. The results are shown in Table 6.

Band gap: Eg=hc/absorption edge wavelength (the Planck's constant: h=6.626×10⁻³⁴ Js, light velocity: c=3×10⁸ m/s)

(Observation of Phase Separation Structure)

A phase separation structure of a phase containing an electron donor compound and a phase containing an electron acceptor compound in the active layer after formation of the active layer on the substrate as described in “Preparation and Evaluation of Photoelectric Conversion Element” above was observed using a 20 eV loss image obtained by an electron energy-loss spectroscopy (TEM-EELS) with a transmission electron microscopy (TEM). The slit width during photographing of the 20 eV loss image was 10 eV.

A substance obtained by applying dropwise a polyvinylpyrrolidone aqueous solution to the film formed by a spin coating method followed by drying and separating was floated in water, and scooped by a grid for TEM, to obtain a sample for TEM observation. In the observation, TEM (JEM2200FS, manufactured by JEOL Ltd.) was used at an acceleration voltage of 200 kV and a 20 eV loss image of a layer within a range of 824 nm×824 nm with 1024×1024 pixels at a magnification of 20000 was used.

(Method for Calculating Junction Length)

A junction length was calculated by a method including the following steps using computer hardware and software.

-   -   Step (i): A computer read an obtained 20 eV loss image (TEM         image) using ImageJ (image processing software).     -   Step (ii): The computer converted the read image to a 16-bit         grayscale image using ImageJ.     -   Step (iii): The computer executed background correction of the         converted 16-bit grayscale image under a condition of a rolling         ball radius of 20 pixels.     -   Step (iv): The computer applied a median filter of 12 pixels to         the image subjected to the background correction (12 pixels).     -   Step (v): The computer executed binarization for the image         processed by the median filter using Otsu's method.     -   Step (vi): The computer extracted an interface on the image         binarized by processing with a command of Find Edge.     -   Step (vii): The computer calculated the area of the interface         extracted by processing with a command of Measure.     -   Step (viii): The computer divided the area of the obtained         interface by a length of one pixel to obtain a result as “length         of interface.”     -   Step (ix): The computer divided the obtained length of the         interface by a visual field area to determine the junction         length per unit area. The results are shown in Table 6.

Examples 2 to 8 and Comparative Examples 1 to 16

A photoelectric conversion element was prepared in the same manner as in Example 1 described except for using each of the inks (I-2) to (I-8) and (C-1) to (C-16) and evaluated.

The results are shown in Table 6.

TABLE 6 Specific dark Band gap of current the p-type (Dark current Junction semiconductor at −5 V/ length material Dark current Ink (μm) (eV) at −2 V) Example 1  I-1 167.9 1.38 4.3 Example 2  I-2 140.5 1.38 1.7 Example 3  I-3 169.1 1.38 2.1 Example 4  I-4 130.3 1.24 8.1 Example 5  I-5 136.4 1.24 5.1 Example 6  I-6 148.1 1.18 6.2 Example 7  I-7 127.3 1.18 1.1 Example 8  I-8 136.2 1.18 8.2 Comparative C-1 186.5 1.38 14.0 Example 1 Comparative C-2 199.2 1.38 17.8 Example 2 Comparative C-3 139.2 1.38 97.6 Example 3 Comparative C-4 121.9 1.38 57.4 Example 4 Comparative C-5 148.0 1.38 43.6 Example 5 Comparative C-6 116.1 1.24 25.6 Example 6 Comparative C-7 159.1 1.59 16.6 Example 7 Comparative C-8 166.6 1.59 22.5 Example 8 Comparative C-9 100.7 1.80 21.2 Example 9 Comparative  C-10 119.4 1.80 43.6 Example 10 Comparative  C-11 135.5 1.80 27.5 Example 11 Comparative  C-12 141.6 1.80 57.4 Example 12 Comparative  C-13 141.7 2.10 36.7 Example 13 Comparative  C-14 157.9 2.10 44.5 Example 14 Comparative  C-15 145.9 2.10 112.5 Example 15 Comparative  C-16 139.3 2.10 19.2 Example 16

In all the photoelectric conversion elements in Examples 1 to 8 in which the junction length was 120 μm to 170 μm, the band gap of the p-type semiconductor material was 0.5 eV to 1.58 eV (0.50 eV to 1.58 eV), and a C₆₀ fullerene derivative was used as the n-type semiconductor material, the specific dark current was less than 10, which was significantly lower than those of the photoelectric conversion elements in Comparative Examples 1 to 16 in which one or both of the junction length and the band gap were not satisfied.

The specific dark current of the photoelectric conversion elements according to Examples are low, that is, the variation in specific dark current when the applied voltage is changed from −2 V to −5 V is low. Therefore, the photoelectric conversion elements can be especially suitably used as a photodetector (photodiode).

EXPLANATIONS OF LETTERS OR NUMERALS

1 Image detection portion

2 Display device

10 Photoelectric conversion element

11, 210 Supporting substrate

12 Anode

13 Hole transport layer

14 Active layer

15 Electron transport layer

16 Cathode

17, 240 Sealing substrate

20 CMOS transistor substrate

30 Interlayer insulating layer

32 Interlayer wiring portion

40 Sealing layer

50 Color filter

100 Fingerprint detection portion

200 Display panel portion

200 a Display region

220 Organic EL element

230 Touch sensor panel 

1. A photodetector used with a reverse bias voltage applied, comprising: an anode; a cathode; and an active layer provided between the anode and the cathode, wherein the active layer contains a p-type semiconductor material having a band gap of 0.5 eV to 1.58 eV, and an n-type semiconductor material, the n-type semiconductor material is a C₆₀ fullerene derivative, and on an image obtained by binarizing an image of the active layer observed by a transmission electron microscope, a junction length between a phase of the n-type semiconductor material and a phase of the p-type semiconductor material is 120 μm to 170 μm per square micrometer of area of the binarized image.
 2. The photodetector according to claim 1, wherein the p-type semiconductor material is a polymer compound having a constitutional unit containing a thiophene skeleton.
 3. The photodetector according to claim 1, wherein the C₆₀ fullerene derivative is C60PCBM.
 4. (canceled)
 5. An image sensor comprising the photodetector according to claim
 1. 6. A fingerprint authentication device comprising the photodetector according to claim
 1. 7. A method for producing a photodetector used with a reverse bias voltage applied, comprising an anode, a cathode, and an active layer provided between the anode and the cathode, comprising: forming the active layer comprising a step (i) of applying an ink containing an n-type semiconductor material, a p-type semiconductor material having a band gap of 0.5 eV to 1.58 eV, and a solvent to a subject to be applied, to obtain a coating film, and a step (ii) of removing the solvent from the coating film, wherein the n-type semiconductor material is a C₆₀ fullerene derivative, and on an image obtained by binarizing an image of the active layer observed by a transmission electron microscope, a junction length between the n-type semiconductor material and the p-type semiconductor material is 120 μm to 170 μm per square micrometer of area of the binarized image.
 8. The method for producing a photodetector according to claim 7, wherein the bandgap of the p-type semiconductor material is a 1.18 eV to eV 1.58.
 9. The method for producing a photodetector according to claim 7, wherein the p-type semiconductor material is a polymer compound having a constitutional unit containing a thiophene skeleton.
 10. The method for producing a photodetector according to claim 7, wherein the C60 fullerene derivative is C60PCBM.
 11. The photodetector according to claim 1, the bandgap of the p-type semiconductor material is 1.18 eV to 1.58 eV. 